Technical Field
The present disclosure relates to a corrosion resistant coating composition for a metal substrate, and an electrodeposition method for the production thereof. More specifically, the present invention relates to a metal substrate coated with a layer containing a phosphate corrosion inhibitor and a layer containing nickel nanoparticles of desirable microstructure and a method employing a pulse electrodeposition solution technique to form a coated metal substrate having improved corrosion resistance.
Description of the Related Art
The “background” description provided herein is for the purpose of generally presenting the context of the disclosure. Work of the presently named inventors, to the extent it is described in this background section, as well as aspects of the description which may not otherwise qualify as prior art at the time of filing, are neither expressly or impliedly admitted as prior art against the present invention.
Nickel (Ni) is commonly employed to enhance surface properties of various materials using electroless nickel plating or electrolytic methods [D. Pletcher, F. C. Walsh, Industrial Electrochemistry, 2nd edition, Chapman and Hall, London, 1990; and J. K. Dennis, T. E. Such, Nickel and Chromium Plating, Butterworth, London, 1986; A. Ul-Hamid, H. Dafalla, A. Quddus, H. Saricimen and L. M. Al-Hadhrami (2011), Electrochemical deposition of Ni on an Al—Cu alloy, J. of Mat. Eng. and Perf. doi: 10.1007/s11665-010-9816-9. —each incorporated herein by reference in its entirety]. Nickel is a preferred choice for coatings due to its strength and resistance to surface degradation as well as due to its visual appeal. The electrolytic method of deposition is selected when it is necessary to have some control over the crystallite size, surface morphology and orientation of Ni, which in turn can significantly affect the surface related properties of the coatings. Conventionally, Ni coatings have been prepared using direct current (dc) electrochemical methods [J. R. Tuck, A. M. Korsunsky, R. I. Davidson, S. J. Bull, D. M. Elliott, Surf. Coat. Technol. 127 (2000) 1; and K. C. Chan, W. K. Chan, N. S. Qu, J. Mater. Process. Technol. 89-90 (1999) 447; and H. Zhao, L. Liu, J. Zhu, Y. Tang, W. Hu, Materials Letters 61 (2007) 1605-1608; and A. Ul-Hamid, Abdul Quddus, F. K. Al-Yousef, A. I. Mohammed, H. Saricimen and L. M. Al-Hadhrami (December 2010) Microstructure and Surface Mechanical Properties of Electrodeposited Ni Coating on Al 2014 alloy, Surface and Coatings Technology, Vol. 205 (7) pp. 2023-2030. —each incorporated herein by reference in its entirety]. More recently, the use of pulse electrodeposition has become popular since it results in Ni coatings with refined grain structure [A. M. El-Sherik, U. Erb, J. Mater. Sci. 30 (1995) 5743; and A. M. El-Sherik, U. Erb, J. Page, Surface and Coatings Technology 88 (1996) 70. —each incorporated herein by reference in its entirety] with attractive corrosion [R. Rofagha, R. Langer, A. M. El-Sherik, U. Erb, G. Palumbo, K. T. Aust, Scripta Metallurgica et Materialia, 25/12, 1991, 2867; and R. Mishra, R. Balasubramaniam, Corrosion Science 46 (2004) 3019; and C. Yang, Z. Yang, M. An, J. Zhang, Z. Tu, C. Li, Plat. Surf. Finish. 88 (5) (2001) 116. —each incorporated herein by reference in its entirety] and tribological properties [Y. Xuetao, W. Yu, S. Dongbai, Y. Hongying, Surface & Coatings Technology 202 (2008) 1895; and R. Mishra, B. Basu, R. Balasubramaniam, Materials Science and Engineering A 373 (2004) 370; and Y. F. Shen, W. Y. Xue, Y. D. Wang, Z. Y. Liu, L. Zuo, Surface & Coatings Technology 202 (2008) 5140; and D. H. Jeong, F. Gonzalez, G. Palumbo, K. T. Aust and U. Erb, Scripta mater. 44 (2001) 493; and Li Chen, L. Wang, Z. Zeng, T. Xu, Surface & Coatings Technology 201 (2006) 599; and A. Ul-Hamid, H. Dafalla, A. Quddus, H. Saricimen, L. M. Al-Hadhrami (June 2011) Microstructure and Surface Mechanical Properties of Pulse Electrodeposited Nickel, Applied Surface Science, doi:10.1016/j.apsusc.2011.04.120. —each incorporated herein by reference in its entirety].
Pulse plating is undertaken when current is applied in repetitive (i.e. pulse on—pulse off) square wave fashion rather than continuously as in dc plating. During pulse electrodeposition, peak current density, pulse on-time, and pulse off-time are accurately controlled. Advantages of pulse electrodeposition include its cost effectiveness and the high current density, power, and range of pulse waveforms available for plating [R. J. C. Choo, J. M. Toguri, A. M. El-Sherik, U. Erb, J. Appl. Electrochem. 25 (1995) 384. —incorporated herein by reference in its entirety]. Pulse electrodeposition results in fine nanostructured coating which show improvement in properties such as hardness, wear, abrasion, coefficients of friction, etc. compared to those produced by conventional dc plating.
Studies of the corrosion behavior of nanostructured coatings are of considerable interest due to their potential use as protective coatings in a wide range of applications. The fine grain structure of nanocoatings results in a high volume fraction of intergranular defects due to the increased density of grain boundaries and triple junctions. There is a concern that this could have an adverse effect on the localized corrosion behavior of nanocoatings. However, previous studies have shown that Ni base nanocoatings are resistant to corrosion. Some studies report an improvement in corrosion resistance while others show behavior comparable to polycrystalline Ni. It has also been reported that nanocrystalline Ni exhibits active-passive-transpassive polarization characteristics similar to that of coarse grained polycrystalline Ni.
In view of the forgoing, one object of the present disclosure is to provide a corrosion resistant coating composition for a metal substrate with an active inhibitor layer underneath nickel that can provide added protection from corrosion. A further aim of the present disclosure is to provide a method for forming the corrosion resistant coating composition comprising electrodepositing Ni (using both direct current and pulse electrodeposition techniques) to adhere a structurally appropriate Ni layer effectively to an inhibitor coated metal substrate. A further aim of the present disclosure is to provide a coated metal substrate as well as a method for inhibiting the corrosion of a metal substrate that includes applying the coating composition described herein.